1. Field of the Invention
This invention relates to a system for securing access to equipment connectable to a telephone communication channel.
2. Description of the Related Art
Telephone communication channels provide effortless access to a wide range of equipment. For example, the simple placement of a telephone call can give an authorized user access to a facsimile machine, computer system, cellular telephone, security alarm system, answering machine, or pager. Also, the simple placement of a telephone call can give authorized technicians, as well as machines, access and means to troubleshoot equipment located in remote or inaccessible locations. However, in the same manner, unauthorized users can gain access to the equipment.
The prior art utilizes data encryption schemes, confidential access codes, or access alarms to prevent unauthorized access to, for example, a computer system. While these methods can be effective, a determined, unauthorized user can defeat these methods by using another computer system. The unauthorized user, having obtained access to the computer system, can further obtain confidential information, erase or change information stored on the computer system, or use the computer system to gain access to other systems.
Also, as exemplified in U.S. Pat. No. 4,763,351, the prior art utilizes control signals to prevent unauthorized access. In this method, a first unit at the authorized user's location generates a control signal received at a second unit at the computer's location. The circuits of both units are complex, and the second unit's circuit must be calibrated to the particular control signal being sent from the first unit. Also, in order to use this method, two telephone lines must be available at the authorized user's location.